Grass mowing machines such as greens mowers or fairway mowers on golf courses may have a hydraulic circuit with hydraulic pumps driven by an internal combustion engine. The hydraulic circuit may include sub-circuits such as a mowing sub-circuit to rotate motors on several cutting units and a raise/lower sub-circuit to move the cutting units between a raised position and a lowered position.
It is desirable to operate grass mowing machines at slower engine speeds to reduce vehicle noise and fuel consumption. However, it also is desirable to maintain rotational speed for the cutting units. Otherwise slow blade rotation would reduce cutting unit performance. A grass mowing machine with a hydraulic circuit is needed that maintains rotational speed for multiple cutting units at reduced engine speeds.